1. Field of the Invention
The present invention relates to intraoral dental imaging. More specifically, the invention is a quality assurance phantom for intraoral digital dental imaging and related method.
2. Description of the Related Art
The degree of servicing dental radiographic equipment varies from office to office and institution to institution. The level of monitoring radiology equipment varies from one jurisdiction to another and range from unknown, annually, every five years, and, in some instances, only when a problem is encountered. As a result, some radiographic imaging systems can be significantly out of tolerance while still in clinical use. The objective of any quality assurance program is to ensure accurate diagnosis and to ensure that doses are kept as low as reasonably achievable (ALARA). This requires a system of regular monitoring procedures to ensure that the various components of the imaging system function within the manufacturer's recommended tolerances.
Most states and regulating bodies have guidelines which state that regular quality assurance of all dental radiographic equipment be performed. Similar guidelines have been advocated by the American Academy of Oral and Maxillofacial Radiology and the American Dental Association. This means regular testing to detect equipment malfunctions, planned monitoring, and scheduled maintenance to produce consistent diagnostic radiographic images. All dental facilities using x-ray equipment, from a simple intraoral dental unit to an advanced three-dimensional imaging system, such as cone beam computed tomography, will benefit from adopting a quality assurance program.
Any intra-oral digital imaging system comprises essentially three components: an x-ray source; a digital image acquisition component (e.g., solid-state sensor or PSP plate and scanner; and an image display component (e.g., a computer or monitor). Each of these components needs to be regularly monitored for performance and function as part of the quality assurance program.
The digital image acquisition component can be evaluated either qualitatively or quantitatively using a radiographic phantom designed to produce a digital image containing information related to fundamental imaging characteristics. These include spatial resolution, contrast resolution or dynamic range, contrast/detail resolution, field uniformity, saturation, and signal to noise response.
One dental radiographic phantom was designed primarily for conventional x-ray film and is commercially available from Fluke Biomedical, formerly Medi-Nuclear Corporation, as the CDRH Dental Image Quality Test Tool. The phantom was developed as a joint collaboration between the Food and Drug Administration (FDA) Center for Devices and Radiological Health (CDRH) and Conference of Radiation Control Program Directors. The phantom consists of a wooden cradle (to hold the test tool body), built-in slots (for attenuation filters), a film slot, an exposure chamber holder, and a mounting screw for use with a tripod. The test tool comes with an aluminum step wedge that is designed for evaluating darkroom fog and consistency testing. The step wedge has two slots: one for exposing a film pack and one for evaluating darkroom fog. The film slot also ensures easy, reproducible placement of the film for consistent imaging. The phantom is designed specifically for testing the functionality of dental x-ray units and provides a means of evaluating half-value layer, determining kVp, and assessing overall image quality, including x-ray film processing. The test tool also contains a human tooth to simulate a clinical image.
A second phantom is the Quart Dental phantom, which is designed to monitor high-contrast and low-contrast special resolution. In addition, a Unfors Mult-O-Meter external detector can be inserted into the phantom to measure kVp, dose and exposure time.
A third phantom is the CD Dent phantom, which is comprised of a three-millimeter aluminum sheet with one hundred cylindrical holes. The CD Dent phantom is designed to optimize the radiation dose and image quality.
A fourth phantom is the DIQUAD analyzer, a hexagonally-shaped device comprising an optically-stimulated light dosimeter to measure dose, and several metal filters and a mesh target to assess image quality.